Try symlinks with an empty target

Show io phase name in error message.

use div/mod.

transferred".

I don't generally like changing that sort of thing, but I think this
one was a persistent source of confusion.

most frequently-used ones in here.

Nelson Beebe pointed out that the information about bug tracking was
out of date.

CPU on a local transfer, without achieving anything useful.

if we have not matched!

Drop unused variables.

Turn off -x.

handles different strings.

reduce symbol dependencies between files and therefore make it easier
to write unit tests.  The diff is large, but the actual code changes
are pretty small.